1. Field of the Invention
The present invention relates to a method for manufacturing a stretchable electronic device.
2. Description of the Related Technology
Building electronic circuits on flexible substrates such as plastic has many advantages. The entire system can be made thinner and more lightweight compared to rigid electronics. Due to its flexibility it can also be folded in irregular forms. Flexible circuits are often used in applications where flexibility, space savings, or production constraints limit the use of rigid circuit boards. Flexible circuits can lead up to a large number of new applications such as flexible displays used in foldable reading systems or flexible circuits embedded in textile.
In some applications there is a need for stretchable interconnections for electrically connecting electronic devices and allowing relative movement of the electronic devices with respect to each other. Several methods are known in the state of the art for obtaining such a stretchable electronic device.
US-A-2002/0094701 relates to a stretchable interconnect for electrically connecting electronic devices which are movable relative to one another and a method for making such a stretchable interconnect. In a first process step electronic devices are formed on a substrate, the devices being spaced from each other. Next, a layer of elastic and conductive material, from which the stretchable interconnects will be formed, is deposited uniformly over the substrate. After the metal layer is deposited, it is photolithographically patterned with a pattern which upon removal of the substrate from support of the interconnect conductor will cause the interconnect conductor to form a stretchable interconnect. Preferably, the conductive material has a stress gradient extending through at least a portion of the thickness of the conductor. Preferably, the patterned interconnect is V-shaped.
US-A-2004/0243204 relates to a stretchable electronic device and a method of fabricating stretchable, polymer-based electrically conducting traces. In a first process step, photolithography is used to define at least one microchannel to produce the casting mould. The substrate on which the microchannel is formed is a stretchable polymer body. In a next process step, the at least one microchannel is filled with a conductive media such as conductive ink, such that at least one circuit line is created. The circuit line has a longitudinal component that extends in the longitudinal direction of the device and an offset component that is at an angle to the longitudinal direction. The longitudinal and offset component allow the apparatus to stretch in the longitudinal direction while maintaining the integrity of the circuit line.
Both US-A-2002/0094701 and US-A-2004/0243204 make use of the photolithographic process for creating the stretchable conductive channels. The photolithographic process comprises a number of different process steps. At first a photosensitive material is deposited on the top surface of a substrate. The photosensitive layer is then exposed to light using an appropriate mask. The mask ensures that areas of the photosensitive material are appropriately exposed to the light such that a two-dimensional pattern corresponding to the stretchable interconnects is formed. Next, the appropriate areas are etched away in a number of different etching process steps. The used photosensitive material and etching chemicals depend on the type of substrate for which is it used. The mask defines the form of the formed stretchable interconnects. As a result, the process for creating the stretchable conductive channels differs for different kinds of substrates. Another disadvantage is that for every change of the form of the channel, another mask is needed.